Illustrated Guide to Home Chemistry Experiments

Chapter 9 Laboratory: Introduction to Chemical Reactions and Stoichiometry 175

LABORATORY 9 .4:

SToICHIomETRy of A doUBLE dISpLACEmENT REACTIoN

In a double displacement reaction, two

compounds exchange elements or ionic species

with each other. Double displacement reactions

take the general form AX + BY → AY + BX,

where A and B are cations (positively charged

ions) and X and Y are anions (negatively

charged ions). Note that the reactants combine

in a fixed proportion—1:1 in this case—and that

the products are also in a fixed proportion,

again 1:1 in this case.

RIREEqU d EqUIpmENT ANd SUppLIES

£ goggles, gloves, and protective clothing

£ balance and weighing paper

£ beaker, 150 mL (2)

£ graduated cylinder, 10 mL

£ graduated cylinder, 100 mL

£ stirring rod

£ wash bottle (water)

£ funnel and filter paper

£ ring stand

£ support ring

£ evaporating dish

£ hotplate

£ storage bottle labeled Schweizer’s Reagent

£ copper(II) sulfate pentahydrate (24.97 g)

£ sodium hydroxide (8.00 g)

£ aqueous household ammonia (~70 mL)

£ water

The proportions are not always 1:1. For example, copper(II) sulfate
reacts with sodium hydroxide to form copper(II) hydroxide and
sodium sulfate, according to the following balanced equation:

CuSo 4 (aq) + 2NaoH(aq) → Cu(oH) 2 (s) + Na 2 So 4 (aq)

or, looking at the ionic species:

Cu2+(aq) + So 4 2-(aq) + 2Na+(aq) + 2oH-(aq)
→ Cu(oH) 2 (s) + 2Na+(aq) + So 4 2-(aq)

Note that on both sides of both equations the number of
molecules (or moles) of the cationic species (copper and sodium)
and the anionic species (sulfate and hydroxide) are the same and
that the total net charge is zero.

In this lab, we’ll react solutions of copper(II) sulfate and sodium
hydroxide to produce copper(II) hydroxide and sodium sulfate.
Knowing the mass of the copper(II) sulfate we used and after
determining the masses of the copper(II) hydroxide and sodium
sulfate products, we’ll examine the stoichiometric relationship of
the reactants and products and determine whether our balanced
equation accurately represents the actual reaction.

To illustrate that reactions are useful for practical purposes as
well as learning purposes, we’ll use the copper(II) hydroxide
produced by this reaction as one of the reactants needed to
synthesize a new compound that we’ll use in a later laboratory
session. This compound, tetraamminecopper dihydroxide ,
Cu(NH 3 ) 4 2 , or Schweizer’s Reagent for short, has the
interesting property of being able to dissolve cellulose (for
example, wood pulp, cotton, paper), and is used to produce rayon
and other semisynthetic fibers.

CUTIOA nS

Copper sulfate is moderately toxic. Sodium hydroxide

is corrosive and caustic. Aqueous ammonia is corrosive

and irritating. Wear splash goggles, gloves, and

protective clothing.

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